Monday, March 3, 2014

Science: Central Nervous System

The Central Nervous System - definition and major parts of the brain.

Central Nervous System – contains the brain and the spinal cord. It serves to connect the sensory and motor fibers within the nervous system thus considered as the "integrating center" for all behavior and bodily functions.

Spinal Cord – is the large rope-like segment of nerve tissue extending down the vertebral column, which is approximately as thick as a person’s little finger. Its principal function is to distribute motor fibers to the effector organs of the body and to collect somato-sensory information to be passed on to the brain. Spinal cord is 2/3 as long as the vertebral column and the rest is spinal roots composed of caudal equina.

Brain – has an average weight of 3 lbs. and contrains at least 15 billion nerve cells called neurons

Major Parts of the Brain 

1. Hindbrain
  • Closest to the spinal cord
  • It performs a series of reflex actions such as blinking of the eye and some processes like breathing, heart rate and blood pressure.
Parts of Hindbrain
  1. Medulla Oblongata – or "the bulb," acts as connecting link between the spinal cord and the brain. It plays an important role in automatic activities
  2. Pons – a large bulge in the brain stem that lies above the medulla oblongata. It connects higher and lower levels of the nervous system and is important in sleeping and waking
  3. Cerebellum – is an important organ of motor coordination. It maintains posture, smoothes out and coordinates complex muscular activities such as walking, dancing, balancing)
2. Midbrain
  • Appears as four bumps of the surface of the brainstem. It’s the connecting link between the hindbrain and the forebrain
  • It connects the sensory and motor pathways between the lower and upper portions of the nervous system
  • It has a special role in visual and auditory activities and also controls complex responses such as walking
3. Forebrain
  • Is the most complex and biggest part of thebrain
Parts of the Forebrain
  • Thalamus – serves as the relay station of the brain for incoming and outgoing impulses to the cerebellum. It is also called the major switching point of the brain
  • Hypothalamus – plays an important role in many physiological activities such as sexual behavior, temperature regulation, sleeping, eating, drinking and maintains homeostasis
  • Cerebrum – the seat of consciousness and of the higher mental processes such as language and abstract thinking

Components of the Nervous System - Neurons

Components of the Nervous System

What is Neuron/Nerve Cell

  • The basic structural unit or building block of the nervous system
  • The smallest nerve cell is less than a millimeter in size while the largest may be more than a meter in length
  • Nerve cell holds the secret how the brain works
  • Nerve cell has two specialized functions: [1] to receive signal [2] the longer extension is for transmitting signals
Acethylcholine – is a neurotransmitter or chemical substance that travels across synaptic gap, stimulates the next neuron, carrying the impulse from one neuron to another

Glial cells – are non-neural cells that hold the neurons in place

Myelin Sheath – is the covering on the axons of neurons, which insulate them, making the transmission of impulses faster

Parts of a Neuron

  • Dendrites – receive impulses and carry them toward the cell bodies. These are short branches of fibers branching out like roots from the cell body
  • Axon – carries impulses away from the cell body toward other neurons. These are the longer branches / fibers at the end of a cell body
  • Synaptic Terminals / End Brushes – are fine collaterals at the end of the axon which have small swellings. It does not actually touch the neuron it stimulates. It has a slight space or synaptic gap between the synaptic terminal and the dendrites of the receiving neuron

Types of Neuron

  • Sensory Neurons /Afferent Neurons – transmit impulses received by the receptors to the CNS.
  • Motor Neurons / Efferent Neurons – carry outgoing signals from the brain to the spinal cord to the muscles and glands
  • Interneurons / connector Neurons / Association Neurons – connect neurons between sensory and motor neurons. These also receive signals from the sensory neurons and send impulses to the other neuron. These are found in the brain, eyes and spinal cord only.